The invention concerns a device for withdrawing samples of liquid samples for analytical elements in which the sample is transported in the analytical element in a capillary-active channel from a sample application opening to the determination site for the sample and in which the capillary-active channel is essentially formed by a carrier, a cover and optionally an intermediate layer lying between the cover and carrier. In addition the invention concerns a process for withdrawing a liquid sample into an analytical element with the aid of the said device.
So-called carrier-bound tests are often used for the qualitative or quantitative analytical determination of components of body fluids, in particular of blood. In these the reagents are embedded in corresponding layers of a solid carrier which is contacted with the sample. If a target analyte is present, the reaction of the liquid sample and reagents leads to a detectable signal, in particular a colour change which can be evaluated visually or with the aid of an instrument, usually by reflection photometry.
Test elements or test carriers are often in the form of test strips which are essentially composed of an elongated carrier layer made of plastic material and detection layers which are applied thereto as test fields. However, test carriers are also known which are in the shape of small quadratic or rectangular plates.
Test elements for clinical diagnostics that are evaluated visually or by reflection photometry are frequently constructed like electrochemical sensors and biosensors such that the sample application zone and the detection zone are arranged one above the other in a vertical axis. This mode of construction is problematic. When the test strip loaded with sample has to be inserted into an instrument, for example a reflection photometer, for measurement, potentially infectious sample material can come into contact with parts of the instrument and may contaminate them. Furthermore volumetric dosing can only be achieved with difficulty especially in cases in which the test strips are used by untrained persons for example in the self-control of blood sugar by diabetics.
Recently test elements have become available which provide a capillary channel or gap with the aid of which at least some of the described problems can be solved.
EP-B-0 034 049 concerns a test element in which the sample is applied to a central sample application site for example an opening in a cover and is transported by capillary force to several detection zones which are spatially separated from the sample application site. In this case it is remarkable that a special design for the geometry of the sample application opening which is also described in EP-B-0 010 456 is emphasized as being particularly preferable. A regular hexagonal shape of the sample entry opening in top view is claimed to centre a drop of liquid sample in the opening. This is claimed to facilitate penetration of the sample into the capillary-active channel which is perpendicular to the sample application opening.
Whereas in the described capillary gap test elements the sample is applied through an opening in the test element which is perpendicular to the capillary gap, in other designs the sample liquid is applied directly into the capillary gap parallel to the direction of spread. This is most simply accomplished by the test element having an edge where the capillary gap ends and which is directly contacted with a sample liquid. When contacted with the edge, the sample liquid is taken up by the channel which is capable of capillary liquid transport.
A frequent problem with the latter test elements is that liquid drops which are applied to the sample application opening of the capillary gap are not able to penetrate into the gap. This phenomenon can have different causes. It is conceivable that in the manufacture of such test elements the opening for fabrication reasons does not have the dimensions that are required for a sample drop to enter into the capillary channel for example because the opening has been contaminated or squashed when the test element was cut to length or stamped out. Another reason may be that the hydrophobicity of the materials which are often used to manufacture the said test elements such as for example hydrophobic plastics, impair, delay or prevent penetration of the sample into the capillary gap. For example a liquid drop already does not enter into the inside of a capillary channel or only very slowly if its inner surfaces are indeed hydrophilic but the cut edge is hydrophobic due to the materials used.
The object of the present invention was to eliminate the disadvantages of the prior art.
This is achieved by the subject matter of the invention as characterized in the patent claims.